MIT scientists mapped the dark side of a hot Jupiter exoplanet in amazing detail

Shedding light on the planet's violent water cycle.
Chris Young
An artist's impression of WASP-121b.Mikal Evans/MIT

Astronomers mapped the dark side of a "hot Jupiter" exoplanet in never-before-seen detail, a post from MIT News reveals.

The planet, called WASP-121b's, is tidally locked to its host star, meaning the differences between the light side and the dark side of the planet are incredibly pronounced.

In a new study led by MIT astronomers, published in the journal Nature Astronomy, the researchers outline their method for mapping WASP-121b using altitude-based temperatures and water presence level data collected by the Hubble Space Telescope in 2018 and 2019. The exoplanet, which is located 850 light-years away from Earth, has a fascinating water cycle that changes dramatically depending on whether the water is located on the planet's day or night side.

The daytime side vaporizes water with temperatures of 4,940F, while the nighttime side's temperature of approximately 2,780F is just low enough to allow hydrogen and oxygen atoms to recombine into water molecules. These then make their way back to the dayside, where the cycle is kicked off once again. According to the researchers, this intense water cycle flings water atoms around the planet at speeds of over 11,000 mph. The dark side is also cool enough to harbor iron and corundum clouds, which could result in rainfall composed of liquid gems. 

Shedding light on the dark corners of the universe

The scientists used spectroscopy data procured from Hubble to map. Astronomical spectroscopy is the study of the stellar spectrum of light and other forms of electromagnetic radiation emitted by distant celestial objects. By studying a stellar spectrum, astronomers can discern many properties of distant space objects, including their chemical composition, temperature, density, and mass. In the case of WASP-121b, the MIT-led team had to detect tiny variations in the spectral line that indicated water vapor on the planet's dark side. They used this line as a guide for creating temperature maps, allowing them to compile the most detailed map of the dark side of an exoplanet seen to date. 

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"We're now moving beyond taking isolated snapshots of specific regions of exoplanet atmospheres, to study them as the 3D systems they truly are," said Thomas Mikal-Evans, who led the study as a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research.

The astronomers say that their work represents the first detailed study of an exoplanet's global atmosphere. It provides new insight into the formation of "hot Jupiter" planets, the large space objects that have made scientists reconsider theories of planetary formation. What's more, it may also help to improve our knowledge pertaining to other, more habitable, exoplanets, helping to improve our investigation into the existence of extraterrestrial life.

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